1. Field of the Invention
The present invention relates to devices and methods for repairing aneurysms. More particularly, the present invention relates to a prosthesis comprising a dual tapered stent.
2. Discussion of the Related Art
An endoprosthesis or stent-graft is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, endoprostheses are inserted into the lumen in a non-expanded form and are then expanded autonomously or with the aid of a second device in situ. The endoprosthesis may be self-expanding, or expansion may occur through the use of a catheter mounted angioplasty balloon, in order to shear and disrupt the obstructions associated with the wall components of the vessel and to obtain an enlarged lumen. In the absence of an endoprosthesis, restenosis may occur as a result of elastic recoil of the stenotic lesion.
The endoprosthesis should preferably be of a somewhat rigid design to provide reinforcement support and may be required to be of considerable length in order to extend over a lengthy diseased area. It is difficult to resolve this need for rigidity with the need of having a flexible endoprosthesis which is readily implanted by inserting it through a sometimes tortuous curving path as is often encountered in a percutaneous insertion technique typically used for implantation of endoprosthesis. This is further complicated by the fact that the endoprosthesis must be readily expandable upon implantation to provide support structure.
Although a number of stent designs for use in endoprostheses have been reported, these designs have suffered from a number of limitations. These include restrictions on the dimensions and flexibility of the stent. For example, a stent having rigid ends and a flexible median part is typically formed of multiple parts and is not continuously flexible along the longitudinal axis. Other stents exist that are longitudinally flexible but consist of a plurality of cylindrical elements connected by flexible members. This design has at least one important disadvantage. For example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent or plaque to embolize or move out of position and further cause damage to the interior lining of healthy vessels.